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Biomedical subjects

M D Rifkin

Publications and source records attributed to M D Rifkin.

At least 55 records · Page 3Linked to original sources
PubMed1991

Fatty liver. Chemical shift phase-difference and suppression magnetic resonance imaging techniques in animals, phantoms, and humans.

In vitro animal and human models were used to evaluate the potential of chemical shift magnetic resonance imaging (MRI) for assessing fatty liver. Phantoms of varying fat content were created from mayonnaise-agar preparations. Fatty liver was induced in eight rats by feeding them ethanol for three to six weeks (36% of total calories), whereas eight control rats were fed a normal diet. T1-weighted in-phase and opposed-phase MR images were obtained of the phantoms animals, and 28 human subjects. Additional images obtained in animals included long TR images with in-phase and opposed-phase technique, and hybrid chemical shift water and fat suppression. The rats were killed and histologic status was graded blindly by a hepatopathologist as normal, mild, moderate, or severe fatty change, for correlation with MR grading. Quantitative analysis of MR images included fat signal fraction for animals, and relative signal decrease between in-phase and opposed-phase images for phantom and human data. Phantom in-phase signal increased linearly with respect to fat content, whereas opposed-phase signal decreased linearly. MRI and histologic grading of rat livers were highly correlated, especially when based on water suppression images (r = 0.91, P = .0001). Opposed-phase images were also highly correlated, while fat suppression images were less effective. There was no overlap between MR-derived fat fractions for control (2.6%-5.7%) versus ethanol-fed rats (7.7%-17.9%, P = .0002). Human liver considered to be fatty by visual inspection (n = 8) had higher relative signal decrease than nonfatty liver (n = 22) (P less than .001). Phantom, animal, and human data demonstrate that comparison of T1-weighted in-phase and opposed-phase images is both practical and sensitive in the detection and grading of fatty liver.

Adult↗
PubMed1990

Comparison of magnetic resonance imaging and ultrasonography in staging early prostate cancer. Results of a multi-institutional cooperative trial.

BACKGROUND: In 1987, a cooperative study group consisting of five institutions was formed to determine the relative benefits of magnetic resonance imaging (MRI) and endorectal (transrectal) ultrasonography in evaluating patients with clinically localized prostate cancer (stage Ta or Tb). METHODS: Over a period of 15 months, 230 patients were entered into the study and evaluated with identical imaging techniques. We compared imaging results with information obtained at the time of surgery and on pathological analysis. RESULTS: MRI correctly staged 77 percent of cases of advanced disease and 57 percent of cases of localized disease; the corresponding figures for ultrasonography were 66 and 46 percent (P not significant). These figures did not vary significantly between readers; moreover, simultaneous interpretation of MRI and ultrasound scans did not improve accuracy. In terms of detecting and localizing lesions, MRI identified only 60 percent of all malignant tumors measuring more than 5 mm on pathological analysis and ultrasonography identified only 59 percent. CONCLUSIONS: The MRI and ultrasonography equipment that is currently available is not highly accurate in staging early prostate cancer, mainly because neither technique has the ability to identify microscopic spread of disease. Further evaluation with improved equipment may improve the accuracy of these techniques.

Adult↗
PubMed1990

MRI of aggressive fibromatosis: frequent appearance of high signal intensity on T2-weighted images.

Magnetic resonance imaging of seven patients with eight pathologically proven desmoid tumor tumors was performed and retrospectively reviewed. On T2-weighted images, all but one lesion demonstrated increased signal intensity relative to muscle, and had signal intensity similar to that of fat. The signal was heterogenous in six of these seven lesions. In a patient with synchronous multicentric lesions, light microscopy correlation revealed increased cellularity in one lesion with increased signal intensity and dense collagenous elements in a second lesion, with decreased signal intensity. High signal intensity appears to be typical but nonspecific, and in following these patients could indicate recurrent tumor, superimposed inflammatory process or granulation tissue.

Abdominal Neoplasms↗
PubMed1990

Bone marrow findings on magnetic resonance images of the knee: accentuation by fat suppression.

Long TR/double spin-echo magnetic resonance images of the knee were obtained with and without the use of fat suppression techniques in seven patients with high signal intramedullary lesions. Comparison between images was performed qualitatively and quantitatively. Contrast-to-noise ratios between focal defects and surrounding fatty marrow were higher with fat suppression in all cases. The mean contrast-to-noise ratio for images obtained with fat suppression was 53.6, while for images obtained without fat suppression the mean contrast-to-noise ratio was 17.3 (p less than 0.01).

Adipose Tissue↗
PubMed1990

Variable flip angle imaging and fat suppression in combined gradient and spin-echo (GREASE) techniques.

Conventional "proton density" and "T2-weighted" spin-echo images are susceptible to motion induced artifact, which is exacerbated by lipid signals. Gradient moment nulling can reduce motion artifact but lengthens the minimum TE, degrading the "proton density" contrast. We designed a pulse sequence capable of optimizing proton density and T2-weighted contrast while suppressing lipid signals and motion induced artifacts. Proton density weighting was obtained by rapid readout gradient reversal immediately after the excitation RF pulse, within a conventional spin-echo sequence. By analyzing the behavior of the macroscopic magnetization and optimizing excitation flip angle, we suppressed T1 contribution to the image, thereby enhancing proton density and T2-weighted contrast with a two- to four-fold reduction of repetition time. This permitted an increased number of averages to be used, reducing motion induced artifacts. Fat suppression in the presence of motion was investigated in two groups of 8 volunteers each by (i) modified Dixon technique, (ii) selective excitation, and (iii) hybrid of both. Elimination of fat signal by the first technique was relatively uniform across the field of view, but it did not fully suppress the ghosts originating from fat motion. Selective excitation, while sensitive to the main field inhomogeneity, largely eliminated the ghosts (0.21 +/- 0.05 vs. 0.29 +/- 0.06, p less than 0.01). The hybrid of both techniques combined with bandwidth optimization, however, showed the best results (0.17 +/- 0.04, p less than 0.001). Variable flip-angle imaging allows optimization of image contrast which, along with averaging and effective fat suppression, significantly improves gradient- and spin-echo imaging, particularly in the presence of motion.

Adipose Tissue↗
PubMed1990

Optimization of gradient-echo imaging parameters for intracaval filters and trapped thromboemboli.

Flow-phantom magnetic resonance (MR) gradient-echo (GRE) imaging at 1.5 T was performed on a titanium Greenfield filter containing trapped blood clots with a high concentration of either deoxyhemoglobin (DHb) or methemoglobin (MHb), simulating acute and older thromboemboli, respectively. Flip angle, repetition time (TR), and echo time (TE) were varied, and a contrast-to-noise ratio between trapped clots and flowing fluid (clot-flow contrast) was determined for each set of imaging parameters. Use of very low flip angles (less than or equal to 10 degrees) rendered MHb clots indistinguishable from flowing fluid. In general, DHb clots displayed greater clot-flow contrast than MHb clots regardless of flip angle. With increasing TE values, T2* effect was observed with MHb clots, and magnetic susceptibility artifacts increased. Overall, optimum clot-flow contrast for imaging of both DHb and MHb clots was achieved with a flip angle of 45 degrees-60 degrees, a TR of 50 msec, and the shortest TE possible. Using GRE parameters similar to the optimum parameters determined in vitro, the authors imaged four patients with nickel-titanium Simon filters and one dog with a titanium Greenfield filter. MR imaging was successful in demonstrating filter location, caval patency, and the presence and extent of intraluminal thrombus.

Adult↗
PubMed1990

Zones of the uterus: discrepancy between US and MR images.

The location of the boundaries among the endometrium, inner myometrium (dark), and outer myometrium (intermediate or bright) were compared on T2-weighted magnetic resonance (MR) and intravaginal ultrasound (US) images obtained within 24 hours of each other. Twelve women with normal reproductive cycles underwent a total of 21 pairs of examinations. The endometrium, inner myometrium (junctional zone), and outer myometrium were measured by three independent observers. The endometrial thickness was thinner with MR imaging (6.5 mm with MR imaging vs 7.9 mm with US early in the cycle [P = .001]; 9.9 mm with MR imaging vs 11.3 mm, respectively, late in the cycle [P = .045]). The junctional zone was thicker with MR imaging (4.4 vs 2.3 mm early [P less than .001]; 3.9 vs 2.2 mm late [P = .003]). The combined thickness of the endometrium and junctional zone was thicker with MR imaging (15.5 vs 12.7 mm early [P = .002]; 17.3 vs 15.8 mm late [P = .064]), confirming that the boundary between the junctional zone and outer myometrium is different with MR imaging versus US.

Adult↗
PubMed1990

Magnetic resonance imaging of the prostate and bladder.

Prostate carcinoma is the most common cancer in men and the second most lethal malignancy among the American male population. Nevertheless, it is potentially curable if detected early and treated appropriately. Treatment options vary depending on the extent (stage) of the cancer. MRI has no role as a screening method for prostatic carcinoma because it is expensive, time consuming, and unable to differentiate benign from malignant disease, but it can detect early prostatic cancers in patients with known tumor and can accurately stage these tumors. MRI is becoming the imaging modality of choice for local staging of prostate cancer and is rapidly replacing CT and ultrasonography for this purpose. Treatment protocols for bladder carcinoma also depend on the stage of the tumor. Clinical staging of bladder cancer has been limited. MRI is as good as or better than CT in bladder tumor staging when extravesical tumor involvement is present. MRI also has the potential to become useful in determining the depth of wall invasion in tumors confined to the bladder.

Female↗
PubMed1990

Magnetic resonance imaging of bone marrow: diagnostic value in diffuse hematologic disorders.

Magnetic resonance imaging (MRI) has value in characterizing normal and abnormal bone marrow because of its ability to distinguish fat from other tissues. Due to this advantage, hematologic disorders resulting in alterations of the normal cellular and fatty marrow distribution can be appreciated. In this article, the role of MRI in diffuse hematologic disorders is emphasized. At birth, almost all marrow is cellular, but by age 25, cellular marrow is restricted to the axial skeleton and proximal femoral and humeral metaphysis. The remainder is fatty, consisting of 80% fat, 15% water, and 5% protein. With increased need for hematopoiesis, reconversion from fatty to cellular marrow occurs in many diffuse disease states. Diffuse diseases that affect bone marrow production are divided into four categories representing conditions that affect the pluripotent hematopoietic stem cell. These include stem cell failure resulting in aplastic anemia, uncontrolled stem cell proliferation as exemplified by polycythemia vera, stem cell dysplasia such as sickle cell anemia, and malignant transformations or replacement. The MRI appearance of these disorders is discussed in this article. The use of spin-echo (SE) sequences is the most common approach to bone marrow imaging. With T1-weighted SE images, fatty marrow will appear bright and cellular marrow, with lower fat content, will exhibit a lower density signal. With T2-weighted SE pulse sequences, contrast between fatty marrow and cellular marrow decreases. Contrast between fatty and cellular marrow is enhanced with chemical shift imaging, including Dixon out-of-phase imaging, as emphasized in this article. MRI presents a more global view of the bone marrow than biopsy material and should provide a better understanding of diffuse hematologic disease progression and resolution.

Bone Marrow↗
PubMed1990

MRI of the prostate.

Prostate cancer is the most prevalent malignancy in the world. It is the most frequently diagnosed cancer in the American male population and the second most lethal cancer in American men. However, concurrent benign prostatic hyperplasia occurs in almost all men developing the malignancy (although the two processes are unrelated) and many others who have no evidence of cancer. Imaging evaluation of the prostate can be for diagnostic or staging purposes. While MRI can be used on occasion for diagnostic evaluation of prostatic disease, it is most often reserved for evaluation of men with known pathology. The use of MRI is important to plan the appropriate therapeutic approach to men with prostate cancer. An understanding of the newer concepts of anatomy, origins of disease, spread of cancer, and the clinical implications of pathological change of the prostate are important and are discussed in this article. The uses of MRI, the deficiencies of the study, the techniques needed to utilize the modality appropriately, and diagnostic criteria and limitations are also discussed.

Humans↗
PubMed1990

Recent advances in magnetic resonance imaging of the knee.

The examination of the knee has rapidly become the most important non-neurologic application of MR imaging. The widespread availability of high signal-to-noise knee coils has made routine imaging with T2-weighted sequences in both coronal and sagittal planes possible in 30 minutes. The spin-echo sequence remains the most important imaging technique, although many newer sequences have also been applied to the knee, with varying degrees of success. Important pitfalls in diagnosis, such as high signal intensity in the posterior horn of the medial meniscus and the transverse meniscal ligament, displaced buckethandle meniscal tears, and discoid menisci, can be recognized with experience. Common clinical problems that are encountered include meniscal cysts, osteonecrosis, and bone bruises. Detection of subtle injuries of the medial collateral ligament, patellar tendon, and anterior cruciate ligament requires careful observation. Intra-articular loose bodies can be reliably detected with MR imaging, and it should be recognized that localized pigmented villonodular synovitis can sometimes simulate the appearance of a loose body. MR imaging is a valuable noninvasive procedure that is complementary to arthroscopy in the evaluation of diseases of the knee.

Humans↗
PubMed1989

Staging of rectal carcinoma: prospective comparison of endorectal US and CT.

One hundred two consecutive patients undergoing surgical treatment for rectal cancer were examined by means of endorectal ultrasound (US) for staging before surgery. Eighty-one of these patients also underwent staging with computed tomography (CT). The diagnostic sensitivity of endorectal US in detection of tumor extension into fat was 67%; specificity, 77%; positive predictive value, 73%; and negative predictive value, 72%. The sensitivity of CT for this finding was 53%; specificity, 53%; positive predictive value, 56%; and negative predictive value, 50%. The sensitivity of endorectal US in detection of lymph node infiltration was 50%; specificity, 92%; positive predictive value, 68%; and negative predictive value, 84%. For this finding the sensitivity and negative predictive value, 76%. These findings suggest that endorectal US may be as accurate as CT, or more so, in the preoperative staging of rectal cancer.

Adipose Tissue↗
PubMed1989

Echogenicity of prostate cancer correlated with histologic grade and stromal fibrosis: endorectal US studies.

In this study an attempt was made to clarify some of the causes of the apparent differences in appearance on ultrasound (US) images of prostate cancer. These differences were correlated with histologic grade and the degree of stromal fibrosis present. Fifty-one cancers (diagnosed and evaluated by means of US-guided biopsy or evaluated by means of radical prostatectomy) were studied. There were 30 hypoechoic, ten echogenically mixed, six isoechoic, and five subtly hyperechoic cancers. The degree of stromal fibrosis was minimal in well-differentiated cancers and increased in poorly differentiated cancers. In addition, the more hypoechoic lesions were, in general, the better-differentiated cancers and had less fibrosis. There was a tendency for the isoechoic cancers and those with subtly hyperechoic areas to more often have poor cellular differentiation and a greater degree of stromal fibrosis, but considerable overlap among histologic types was seen.

Fibrosis↗
PubMed1989

Morton neuroma: sonographic evaluation.

One hundred consecutive patients with symptoms suggestive of Morton neuroma were examined with sonography, and 134 intermetatarsal masses were demonstrated. Forty-five patients underwent surgical exploration, which revealed Morton neuromas. The typical sonographic appearance is that of an ovoid, hypoechoic mass oriented parallel to the long axis of the metatarsals. Most masses were between the second and third or third and fourth metatarsals and seemed to produce symptoms when reaching a diameter of 5 mm.

Adult↗